Fuel pump and filter replacement 1990 560SEC
DIY videos-fuel system
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It's nice to see people try to help others to maintain their CIS-E cars and I'm sure that the videos in this thread are posted with this laudable aim. I'm also sure that many viewers think that these videos hold professional information & advice. But having been involved as a young design engineer in Mercedes' CIS-E engines in the 1980's, I assure this forum that CIS-E related YouTube videos often hold incorrect information & inadvisable advice. ... Let me take the above video (from post 18) as an example:
At 3:33 the man in the video says:
“The control pressure is the pressure that is fed through these 8 lines to the injectors“
^This is not correct. The “control pressure“ only exists in the lower chambers of the differential pressure valves and is not fed to the injectors. There is not even any hydraulic connection between the lower chambers and the injector lines.
3:48 and 42:35:
“This is the idle mixture adjuster“ and “This is the idle mixture adjustment...“
He uses ^these misleading names for the adjustment tower. The fact that the FSM department people simply adopted the name of that adjustment screw, namely “Gemischregulierschraube“ (mixture regulating screw) from the K-Jetronic manual in the KE-Jetronic manual doesn‘t make it less misleading. … On the KE-Jetronic, besides a short after-start & warm-up phase & WOT, the a/f mixture isn‘t even changed via this “adjuster“, unless the systems Lambda leaning or enriching limit (0% or 100% duty cycle) is exceeded, which is completely inadvisable, of course.
In my KE-Jetronic Lambda Control Thread I explained in detail what the actual purpose of this adjustment screw was & still is … (and when & when not to use it
).10:35
“The basis of this system is extremely simple“
In the past ~35 years I‘ve met a number of people who said ^this or something similar. It turned out that none of them actually understood this system.
10:48
“The fuel goes into this bottom chamber“
There is no such thing as “the bottom chamber". The FD has as many “lower chambers“ & “upper chambers“ as the engine has cylinders and only a very small part of the fuel that enters the FD goes into the lower chambers.
27:50
“If you have a car that is stumbling off the line… … you turn this screw in ¼ of a turn in“
^This should certainly not be done ! … If you have a car that is stumbling off the line, you should rather search for & fix the cause of that behavior, instead of masking it via this screw.
35:10
“The pressure that is being fed to the system and the pressure that is being fed to the injectors should have a difference at idle of about 0.4 bar.“
^This is not correct. … “0.4 bar“ is the nominal pressure difference between SP (system pressure) and LCP (lower chamber pressure). And LCP is not the pressure that is being fed to the injectors. As I said above (at 3:33), there is not even any hydraulic connection between the lower chambers and the injectors.
36:05
“The difference between the upper and lower chamber… …0.4 bar“
Again … 0.4 bar is the difference between SP (measured at the upper test port) and LCP (measured at the lower test port). The “upper chamber pressure“ can not even be measured at all. … For proper diagnosis it is important to know the role that the upper chamber pressure plays, though !
38:00
He suggests to “turn the EHA adjustment screw ¼ out, if that pressure difference is only 0.3 bar“.
What should be done first in the case he describes is to search for the cause of this smaller pressure difference, instead of masking it via EHA adjustment screw !
42:50
“I‘m gonna make it really simple for you. Adjust the car to where it has the smoothest idle, the best starting and does not stumble off the line. That is a happy KE-Jetronic Mercedes.“
^This should definitely not be done ! … That would be a “KE-Jetronic Mercedes“ with (possibly many) problems masked via Lambda adjustment screw.
… The problems he mentions before & after that statement refer to causes that should be checked & fixed, instead of being masked via that adjustment screw ! … And don‘t let yourself be tricked into believing that you did the right thing, if after fiddling around with that adjustment screw the car behaves better ! … You just mask problems that way, with negative effects on the engine‘s health each time when Lambda control is not active. Plus you deprive yourself from a lot of valuable & revealing (yet widely ignored) diagnostic information that way.46:40
“That‘s why they call this the air/fuel ratio adjustment. They also call it the CO2 adjustment or idle mixture adjustment.“
They call it that, because they don‘t know what its actual purpose is. …
I say ^these things not to criticize anybody but because they‘re important to know for quick & targeted CIS-E related diagnosis and proper maintenance … which, unfortunately, hardly takes place here at BenzWorld. And fiddling around with adjustment screws in order to make problems go away, instead of taking care of their causes is not what I call proper maintenance ! … Over here in ‘BenzCountry‘ that‘s called “Pfuscherei“ (botchery).
I may be too short of time to respond to disagreements / questions. For more details I recommend to have a close look at CIS-E related posts of mine here in this forum (particularly in my KE-Jetronic Lambda Control Thread).
Anyway, I warmly recommend those who want to keep their “KE-Jetronic Mercedes“ in proper condition to beware of CIS-E related YouTube videos ! ...
H.D.
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